Question

A wooden sled of mass 100 kg sits on wet snow (µ_s=0.14,?_k=0.1).

Calculate magnitude of the friction if it is being pushed horizontally by a 90N force.

Calculate the magnitude of the friction if it is being pulled by a 150N force inclined at 30 degrees from the horizontal.

Please show and explain formulas

Answer 1

Here,

m = 100 Kg

maximum static friction when force is extered horizontally

fmax = 0.14 * 100 * 10

fmax= 140 N

Now as the applied force is less than 140 N

frictional force is equal to applied force

the frictional force is 90 N

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for 150 N at 30 degree

Normal force , N = 100 * 10 - 150 * sin(30)

N = 925 N

maximum static friction

fmax = 925 * 0.14 = 129.5 N

applied horizontal force = 150 * cos(30) = 129.9 N

as this is greater than the maximum friction

kinetic friction will act

friction force acting = 925 * 0.10

friction force acting = 92.5 N

the friction acting is 92.5 N